The problem of measuring interior profiles such as tunnels by purely optical means has been discussed in U.S. Pat. No. 3,950,096 (Aeschlimann et al). This patent proposed the use of at least one laser beam to be projected onto a tunnel wall and an image analyser and optical system arranged so as to capture the spot appearing on the wall. The information thus derived is representative of the distance from the tunnel center to the impact point of the laser beam.
In order to obtain information representative of a profile it is necessary either to use a plurality of laser beams or to shift the single laser beam so that it impacts a succession of points. In neither case will there be a continuous profile. Where one laser beam only is utilised, the process will be very slow and perhaps unacceptably so when it is necessary to obtain a series of profiles along the length of a tunnel. Should a plurality of laser beams be employed the cost of the equipment will be increased.
A further problem arises when the tunnel is curved along its length or has an irregular floor surface with variable levels. In the known apparatus where such factors have to be taken into consideration both time and precision of measurement will be lost.
The apparatus of this invention, as in the above-mentioned U.S. patent, employs purely optical means for measuring interior profiles, but in view of its novel conception enables examination of predetermined zones or points as well as complete profiles. In view of its high speed acquisition of data it provides a practicable arrangement for measuring a large number of sections.
In carrying out inspection in respect of a master gauge, the programming possible with the novel system of the invention enables giving of immediate warning should there be risk of collision.
During the sequence of profile measurements, electronic processing converts analog type information from the optical system into digital form capable of being readily stored in adequate memory means. It thus becomes feasible at any desired time to employ standard comparison data to obtain graphical representations of possible deformations of the tunnel at predetermined sections thereof along the measured section.